​ Have you ever seen a lizard hurtling over your head? How about a frog sailing down from the tree tops? I’m not making these animals up. They belong to one of earth’s most astonishing groups of animals.

Gliders.

Gliders travel through the air, but they don’t fly. Instead, they glide. What’s the difference? Well, to get itself off the ground, a bird, bat, or insect has to generate a force called lift. A flying animal generates lift using its wings, which are attached to powerful flight muscles. These wings move and bend in complicated motions to counteract the force of gravity.

Gliding animals do not have muscle-powered wings. Instead, most gliding animals have special flaps or folds of skin called patagia. Like wings, the patagia generate lift—but only after the animal is already moving through the air.

When chased by a snake, a Draco lizard leaps from its tree. Instead of plunging to its death, it spreads out its rib cage into two elegant airfoils covered with skin. As air rushes over them, these airfoils—the patagia—generate lift to keep the lizard from falling straight down. The lizard does steadily descend toward earth, but it is also riding the air. It can change directions, pull a U-turn, and control where it wants to go. In the process it can travel hundreds of feet before landing on another tree or on the ground.

The patagia of Wallace’s frogs lie between their toes. These frogs usually live up in the trees, but when it is time to mate or lay eggs, they leap, spread out their toes, and glide to earth.

Earth’s most astonishing gliders may be five species of gliding snakes. These snakes don’t have patagia. Instead, they flatten out their bodies and “crawl” through the air. Scientists aren’t sure if the crawling motion helps generate lift, or if lift comes mainly from a snake’s flattened shape, but the animals can glide more than 100 feet before landing.​ Most of earth’s gliding animals live in Southeast Asian rainforests, which are home to more than eighty species of gliding lizards, frogs, snakes, and mammals. In North America, we have only two gliding animals: Northern and Southern flying squirrels. Despite their name, flying squirrels don’t fly. They glide—and are adorably cute! Want to see one? Try shining a flashlight on a bird feeder at night!

A male Draco lizardextending his gular flag (throat flap) and patagi (wings). While not capable of powered flight Dracos often obtain lift in the course of their gliding flights. Glides as long as 200 feet have been recorded,Wikimedia

Wallace's frogs live almost exclusively in the trees, and leap and "fly" from tree to tree or to bushes. The membranes between their toes and loose skin flaps on their sides catch the air as they fall, helping them to glide, sometimes 50 feet or more, to a neighboring tree branch or even all the way to the ground. They also have oversized toe pads to help them land softly and stick to tree trunks. Wikimedia

Flying squirrelsare able to glide from one tree to another with the aid of a patagium, a furry, parachute-like membrane that stretches from wrist to ankle. Their long tail provides stability in flight. Wikimedia

There are five recognized species of flying snake, found from western India to the Indonesian archipelago. They flatten out their bodies and parachute or glide using their ribs to become flat, and then they whip their bodies in a fast, rhythmic S-shape to stay airborne. Wikimedia

​Illustrated with arresting photographs, Sneed B. Collard's Catching Air: Taking the Leap with Gliding Animalstakes us around the world to learn why so many gliders live in Southeast Asia, and to find out why this gravity-defying ability has evolved in Draco lizards, snakes, and frogs as well as mammals. Why do gliders stop short of flying, how did bats make that final leap, and how did Homo sapiens bypass evolution to glide via wingsuits and hang gliders―or is that evolution in another guise?

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